Micro-lesson · Module 2
Greater potency does not establish clinical superiority
Compare potency and maximum response within a defined assay.
Educational information for healthcare professionals and the general public. Not individual medical advice, diagnosis, treatment, or a recommendation to use a compound.
Learning objective: Compare potency and maximum response within a defined assay.
The concept
Potency compares the concentration needed to achieve a predefined response. In an experimental curve, it is often summarized as an EC50. In the specified assay, a relative EC50 is the concentration producing a response halfway between that compound’s fitted lower and upper response limits. With a zero baseline, this is half its own maximum response. Different response limits mean that equal relative fractions need not represent equal absolute effects. Pharmacological efficacy refers to the ability to produce a response, including the maximum response observed in a system. One agonist may achieve a greater response than another even if it requires a higher concentration. It's important to distinguish between pharmacological efficacy and clinical efficacy.
Check your understanding
Compound A reaches half-maximal response at a lower concentration than compound B. Does that make A the better treatment?
Answer and explanation
Not from that comparison alone. If the two compounds have different fitted response limits, their half-maximal responses need not represent the same absolute effect. It supports a potency comparison under the assay conditions. Maximum response, exposure, adverse effects, and patient-relevant outcomes remain separate questions. A left-shifted concentration-response curve cannot substitute for an appropriate clinical comparison.
Continue learning
Explore Module 2 in PEPTIDE Academy for the complete lesson and further case discussion.
References
Bibliographic sources shown for transparency. Citation verification pending; no citation is marked verified.
- Marino M, Jamal Z, Zito PM. 2023. Pharmacodynamics. Stat Pearls Publishing. Update January 29, 2023. Reference chapter; NBK507791.
- Alberts B et al. 2002. General principles of cell communication. In Molecular Biology of the Cell, fourth edition. Garland Science. Reference chapter; identifier NBK26813.
- Alberts B et al. 2002. Signaling by G protein-coupled surface receptors. In Molecular Biology of the Cell, fourth edition. Garland Science. Reference chapter; identifier NBK26912.
- Reference science. Assay Guidance Manual (NCBI Bookshelf), glossary entry “Relative EC50”. Chapter published April 15, 2012; updated September 22, 2014. NBK92002.
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